1. Field of the Invention
This invention relates to a pressure-sensitive copying paper using as a color former a pyridine-carboxylic acid lactone represented by the formula ##SPC2##
Or a mixture thereof, wherein R.sub.1 and R.sub.2 each represents a hydrogen atom, an acyl group, a lower alkyl group which may be substituted with a halogen atom, a cyano, hydroxyl, lower alkoxy, lower alkylamino, acetyl or phenoxy group, or a benzyl or phenyl group which may be substituted with a lower alkyl group, a halogen atom, a lower alkoxy, nitro, amino or lower alkylamino group, or R.sub.1 and R.sub.2 may, when taken with a nitrogen atom to which R.sub.1 and R.sub.2 are attached, form a part of a saturated hydrocarbon chain of a heterocylic ring; R.sub.3 represents a hydrogen or halogen atom, a nitro, amino, lower alkylamino group or a lower alkyl group which may be substituted with a halogen atom or a lower alkoxy group, a lower alkoxy group which may be substituted with a halogen atom, or a benzyl, benzyloxy or phenoxy group which may be substituted with a halogen atom, a lower alkyl, alkoxy or lower alkylamino group; R.sub.4 represents a hydrogen or halogen atom, a lower alkyl group or a phenyl group; and A represents a carbazolyl, acridinyl, phenothiazinyl, thienyl, thianaphthenyl, morpholinophenyl, julolidinyl or tetrahydroquinolyl group which may be substituted with a lower alkyl, lower alkylamino, acyl or nitro group; the alkyl moiety in said lower alkyl, lower alkoxy or lower alkylamino group containing 1 to 5 carbon atoms.
2. Description of the Prior Art
In general, pressure-sensitive copying paper comprises the combination of an upper sheet paper (or transfer sheet) having coated on the back surface thereof minute microcapsules containing dissolved therein an electron donative substantially colorless organic compound capable of undergoing color reaction, i.e., color former, and a lower sheet paper (or receiving sheet) having coated on the surface thereof a color developer. When these two coated surfaces are brought into contact with each other and a localized pressure is applied to the assembly by handwriting or typewriting, microcapsules located at the pressure-applied area rupture and the organic color former contained in the organic solvent comes into contact with the color developer to form color.
Color developers which can be used in this invention include active clay substances such as acid clay, attapulgite, zeolite, bentonite; solid organic acids such as succinic acid, tannic acid, benzoic acid; and acidic polymers such as phenolformalin polymers, phenol-acetylene polymers, styrene-maleic anhydride polymers containing residual acid groups, salicylic acid-formalin polymers and the like.
As the organic solvent for dissolving the color former, there are ethylene glycol, chlorobenzenes, diethyl phthalate, trioctyl phosphate, dibenzyl benzene, dibenzyl toluene, alkylnaphthalenes and naphthylalkyl alcohols and the like.